Bitumen has developed continually to meet ever-increasing performance demands from for instance building constructors. Advances in building techniques necessitate the development of very high performance roofing felt systems. Such roofing felt systems need to be sufficiently flexible, elastic and resistant to permanent deformation at all service temperatures to accommodate the movement without losing their waterproofing performance.
A known technique to improve the performance of bitumen comprises modifying the bitumen by incorporating into it high levels of a thermoplastic rubber. In this way a higher degree of elasticity and an improved durability can be established.
Another known technique includes subjecting the bitumen to a so-called blowing process, optionally in the presence of a bitumen blowing catalyst, by way of which the temperature susceptibility of the bitumen can be reduced. A combination of the above-mentioned techniques is for instance taught by U.S. Pat. No. 5,342,866 whereby the blowing is carried out under mild conditions and in the presence of a small amount of ferric chloride.
An object of the present invention is to provide a bitumen composition having a higher degree of elasticity and an improved durability when compared with bitumen compositions prepared in a conventional manner. Surprisingly, it has now been found that such bitumen compositions can be prepared by subjecting a particular bitumen mixture to a blowing process.